Window coverings are provided in a wide variety of styles and configurations to both provide the function of at least partially occluding the passage of light through a window and enhancing an appearance of a room in which the window is located. Such window coverings can include shades which are typically continuous from a top rail at an upper end of the window to a bottom rail at a bottom end of the shade. Such shades can be in the form of a single layer of material or multiple layers of material and can be pleated or smooth, and can optionally include cellular “hive-like” cavities within the window covering structure itself. Window coverings also include blinds which are typically formed of separate slats of rigid or flexible material which either have a fixed angle or can be adjusted in angle to allow some light to pass through the separate slats within the blind.
The entire assembly mounted within the window is referred to as the window covering assembly. The portion of the window covering assembly which acts to occlude the passage of light is referred to as the window covering or as the window covering structure. The entire window covering assembly thus includes the top rail, the bottom rail and the window covering structure extending between the top rail and the bottom rail.
While window coverings can be of fixed size, window coverings are usually desirably adjustable so that the window can be blocked when desired or exposed, depending on the needs of the user. Various different prior art window covering adjustment systems are known. Most typically, cords are provided which extend from the bottom rail, through the window covering structure up to the top rail, and then continue on an exterior side of the window covering structure. A user grasps the cords and pulls the cords to raise the bottom rail towards the top rail and expose the window. The user releases the cord and the weight of the bottom rail causes the window covering to cover the window. Often locking mechanisms are also provided to assist in locking the bottom rail of the shade at a desired position.
Such external cord based window covering adjustment mechanisms are less than entirely satisfactory. The cords can become entangled with themselves or other structures, rendering the cords non-functional in adjusting the position of the window covering. The cords present a safety risk for infants and toddlers. Also, the locking mechanisms for locking the cord in the desired position so that the window covering bottom rail is positioned where desired is often difficult to use effectively and is prone to wearing out, so that the window covering is effectively stalled in either the fully open or fully closed position.
The deficiencies in external cord systems for adjusting window covering position have led to the development of “cordless” window coverings. For instance, see U.S. Pat. No. 6,644,375. Such cordless window coverings include cords which are internal, extending between the top rail and the bottom rail but with no external cords. Some such cordless blinds utilize locking mechanisms adjacent the top rail or the bottom rail which are typically in the form of buttons. When the bottom rail is to be raised to expose the window, one or more buttons are pushed and the bottom rail is raised. When the button is released, the shade remains in the selected position. When the bottom rail is to be lowered, the button(s) can again be pushed and the bottom rail repositioned before releasing the button(s) with the bottom rail in the new desired position. In at least one window covering, included in Published Application No. US-2004-0007333-A1, the bottom rail can be pulled down without requiring that the buttons be pushed. Only when the bottom rail is to be raised do the buttons need to be pushed.
Other prior art window coverings have height adjustment mechanisms which rely on some form of balancing of the bottom rail so that adjustment of the height of the shade is somewhat automatic. Instead of requiring that buttons be pushed, the bottom rail is merely repositioned to a desired position. The shade then remains balanced in the new position. For instance, see U.S. Pat. No. 6,571,853.
While such balanced cordless shades are taught in the prior art, such balanced cordless shades have heretofore required complex mechanisms which have exhibited various undesirable performance characteristics. In particular, such cordless balanced shades have typically included some form of cord collecting structure, such as a spool which has been biased, such as with a spring to cause the cord running from the bottom rail up to the cord collector to be encouraged onto the spool. As the bottom rail moves downward, the strength of the spring increases, making it difficult to cause the bottom rail to remain fixed in the lower position. At a minimum, the bottom rail is inclined to bounce somewhat and not remain solidly in a fully down position. When a weaker spring or other biaser is used, it has insufficient force to keep the bottom rail from falling down at least somewhat when the user desires that the window covering be entirely open.
Variable resistance springs have been attempted, as one solution to this problem. Various cord handling mechanisms have been utilized including one-way brakes and one-way cord movement retarders to discourage such undesirable bounce. With each of these solutions, a need remains for a simple and reliable lifting mechanism for a window covering which allows a user to easily adjust a position of the bottom rail of the window covering merely by grasping the bottom rail and positioning it where desired, with confidence that the bottom rail will remain precisely where it has been left until it is again moved by the user.